https://www.theamazonbasin.com/wiki/index.php/Dragon_Tail>+% Fire Skill Damage applies to radial fire attack damage.
I tested that in hero editor previously, its true- % fire skill damage definitely applies to dragon tail. Getting +20000% makes it go from dealing a small fraction of eldritch to killing him and his pack in 1 hit
I didn't actually test to confirm its multiplicative, I just assumed that because it wouldn't make much sense to code it otherwise, but there's always a chance its got some oddball scaling where it its additive with the skill
It does not display on the character screen, but the LCS doesn't really say anything remotely accurate about dragon tail
%ed has a very small impact when you're using tiger strike but it has a very large impact when you're not
Being able to dragon tail for ~20-30k+ hp in damage without tiger strike is really the goal here for good reason, it lets you just spam dragon tail instead of being dependent on charges, which really speeds up kill speed
Its still nice to be able to get 1-3 charges to blow up a boss or champion pack in the combo OHKO, but its slower and more clumsy than just spamming tail for trash mobs.
To give you an idea, against a 15/15% resist monster with 167 strength, a {lacerator, 2020 armor, 2020 shield, 1010 3MA circlet) deals 174k damage with TS but only 19k without charges. Meanwhile a {lacerator, fort, phoenix, 1010 3MA circlet} deals 144k with TS, but 30k without
The balanced build I'd recommend, a 300 strength with {lacerator, enigma, phoenix, 1010 3MA circlet} deals 177k with charges, 29k without, sacrificing some HP to make up the damage.
Well, now I think I have to try making one of these.